That's a tough call I wouldn't consider kendo superior to kendo both have their strenghts on different levels. I have seen several exhibition matches between the two and I can tell you a quick lunge from an experience fencer is deadly. How kendo strikes and counters in close range seem to devestate a fencers ability to attack. I think what it really comes down to is speed percision and footwork. The matches I watched didn't last very long they were over quickly and in one strike. I also noticed how patient they were played a factor. Speed vs power is always an interesting to watch. I tend to be on the fast side in kendo with a long reach iv changed styles but not my overall fighting style I'm very patient and I take advantage of any opening and use a lot feints.
I do agree with you in a narrow space fencing would have the advantage in an open space kendo would have the advantage. It's easy to see why because of the use of each respective weapon. Using a two handed weapon in a narrow space hampers any attack broad and wide strikes won't work but a style that utilizes quick forward lunges and quick foot work for advancing and retreating is perfect. A kendo user in wide open space can utilizes a wide range of moments and free flow easily with mid section and over head attacks.
I'm no expert and of course the out come would depend on a persons skill. Watching two masters go at it would be interesting.
Here are a couple of vids
YouTube - Kendo vs Fencing
YouTube - Kendo vs Fencing
heres an interesting one Kendo vs Escrima
YouTube - Kendo vs Escrima